It won't nuke the trans. The response in that thread talking about the fluid flow through the valve body is under the mistaken impression that moving the shifter from 1 to D will cause it to immediately shift into 3rd gear, and that pulling it back into 1 then causes a downshift back into 2nd. What actually happens is you start off in 1st gear with the shifter in the 1 position. This position will lock the trans in 1st gear if done from a stop, or will lock it in 2nd gear if done from a roll. When you are ready to shift to 2nd gear, moving the shifter to D will allow that shift to 2nd to happen. Now if you again move the shifter back into 1 before the shift to 3rd happens, your trans will stay locked in 2nd gear, until you again move the shifter to D, which will allow the shift to 3rd. Now the only reason to do all this is to make the trans shift at a higher rpm, which is fun, but on a stock engine, likely not any faster than letting it shift on its own, and transmission damage can occur not from the 1-D-1 shuffle itself, but if you rev too high you can balloon the torque converter and also possibly damage other internal transmission parts, but those are things that a different valve body will not solve either.